SVF Multimode

Overview

State Variable Filter (Multimode) with coefficients derived from input pins

Discussion

This module is a State Variable Filter (short "SVF") module using the standard Chamberlin algorithm. The digital state variable filter was described in Hal Chamberlin "Musical Applications of Microprocessors". Derived by straight-forward replacement of components from the analog state variable filter with digital counterparts, the digital state variable is a popular synthesizer filter, as was its analog counterpart. The state variable filter has several advantages over biquads as a synthesizer filter. Lowpass, highpass and bandpass (also band-reject in theory) are available simultaneously. Also, frequency and Q control are independent and their values calculated easily.

Adjust the filter parameters by setting the fields freq and Q. The variable "freq" controls the center frequency of the filter and "Q" determines how sharp the filter is. Low Q values lead to broad filters and high Q values lead to narrow filters. When the parameters frequency or quality are controlled through the input pin, then the default behaviour of the module is to calculate coefficients in the Set function. User can change the behaviour through the parameter setBehavior to calculate coefficients in the Process function itself.

Note: this module has custom frequency response plotting and won’t work when plotted together with other modules in a chain. Only the SVF frequency response will be plotted in this case, and other modules in the chain will error out.

Module Pack

awe-mod-dspc-snd

ClassID

classID = 41805

Type Definition

typedef struct _ModuleSVFMultimode
{
ModuleInstanceDescriptor instance;            // Common Audio Weaver module instance structure
INT32 setBehavior;                            // Controls the Set function calling behavior of the module. 0 = OnChangeDeferredSet, 1 = OnChangeInstantSet
FLOAT32 frequency;                            // Cutoff frequency of the filter, in Hz.
FLOAT32 quality;                              // Specifies the Q of the filter, if applicable.
FLOAT32 g;                                    // g coefficient
FLOAT32 g1;                                   // g1 coefficient
FLOAT32 h;                                    // h coefficient
INT32 updateActive;                           // Specifies whether the filter coefficients are updating (=1) or fixed (=0).
FLOAT32 current_g;                            // Instantaneous g coefficient.
FLOAT32 current_g1;                           // Instantaneous g1 coefficient.
FLOAT32 current_h;                            // Instantaneous h coefficient.
UINT32 pinID;                                 // Specifies which control pins are available.
FLOAT32* state;                               // State variables. 2*numChannels per section.
} ModuleSVFMultimodeClass;

Variables

Properties

Name	Type	Usage	isHidden	Default Value	Range	Units
setBehavior	int	parameter	0	0	0:1
frequency	float	state	0	250	10:23990	Hz
quality	float	state	0	0.7071	0.05:20
g	float	derived	0	0.01636	Unrestricted
g1	float	derived	0	1.431	Unrestricted
h	float	derived	0	0.9771	Unrestricted
updateActive	int	parameter	1	0	0:1
current_g	float	state	1	0	Unrestricted
current_g1	float	state	1	0	Unrestricted
current_h	float	state	1	0	Unrestricted
pinID	uint	const	1	3	Unrestricted
state	float*	state	1	[2 x 1]	Unrestricted

Pins

Input Pins


Name	freqPin
Description	Cutoff frequency of the filter
Data type	float
Channel range	1
Block size range	Unrestricted
Sample rate range	Unrestricted
Complex support	Real


Name	qPin
Description	Q of the filter
Data type	float
Channel range	1
Block size range	Unrestricted
Sample rate range	Unrestricted
Complex support	Real


Name	in
Description	Input signal
Data type	float
Channel range	Unrestricted
Block size range	Unrestricted
Sample rate range	Unrestricted
Complex support	Real

Output Pins


Name	LP
Description	Output signal
Data Type	float


Name	BP
Description	Output signal
Data Type	float


Name	HP
Description	Output signal
Data Type	float

Matlab Usage

File Name: svf_multimode_module.m